Ocean wave energy in most northern and southern global latitudes is several times more concentrated than solar energy, or the surface winds that produce ocean waves. Ocean waves are also more consistent and predictable than wind energy and should, therefore, ultimately result in a lower cost of renewable power. Yet ocean wave energy technical development and commercial deployment lags substantially behind wind (including offshore wind) and solar energy. This is in large part due to the proliferation of possible and proposed methods of converting wave energy into power that has diffused public and private efforts so as to limit resources available to the few WEC concepts that may prove to be both affordable, effective and survivable.
Many WEC concepts utilize circular-section buoy-type surface floats reacting against either a central motion-stabilized vertical spar (called “heave-only buoys” or “spar buoys” including the PowerBuoy and WaveBob WECs), or a seabed affixed tensioned cable. These circular-section buoy-type WECs were initially popular because circular navigation buoys have proven to survive in extreme seas and because early university wave tank experiments using buoy-type “point absorber” WECs showed high capture efficiencies when conditions of “resonance” (matching WEC moving mass to a specific wave amplitude and period) were achieved using wave-tank-generated artificially uniform amplitude and period waves. Point absorber type WEC performance in real random ocean wave environments where “resonance” conditions cannot be established or maintained has been extremely disappointing with wave energy capture efficiencies typically less than ⅓ of that achieved in wave tanks. Because these circular floats move/translate primarily vertically, they are often referred to as “heave only buoys” and capture little or none of the surge (lateral) wave-only component.
During the late 1980's, Salter and others at the University of Edinburgh proposed a spar buoy having a sloped or inclined spar called the “Sloped IPS Buoy”. This design permitted the buoy or float to move along the spar in both an upward and a rearward motion relative to incoming wave crests and return forward and downward on ensuing wave troughs. Wave tank tests published in 1999 by University of Edinburgh doctoral candidate Chia-Po Lin established that this sloped-motion-constrained buoy or float captured both substantial heave and surge wave energy components even in random wave conditions when the spar was maintained in a fixed sloped position via attachment to the tank bottom.
Other early WEC concepts utilize two or more hinged articulating rafts pointed into (transverse to) oncoming wave fronts including the Pelamis, Cockerell Raft, McCabe Wave Pump, and more recently the Crestwing and Columbia Stingray. These “articulating” type WECs have two or more surface floats or rafts hinged at or near the sea surface (Still Water Line or “SWL”) preventing significant lateral float translation or movement and hence limited surge (lateral) wave energy capture. The portion of adjacent rafts or floats near the common hinge joint also limits vertical movement of these portions, which reduces “heave” wave energy capture.
The “elongated swing arms” or “dual swing arms” or “compound motion arms” that float relative to fixed or stabilized frame linkages of the disclosure substantially improve the performance of all “articulating raft” type WECs. The disclosure improves both heave wave energy capture (by allowing more vertical movement/translation near the float/raft surface hinge) more surge (lateral) wave energy capture by increasing lateral float, raft movement, or translation.
Other early concepts, called oscillating water columns or OWCs, use shore attached, or off-shore floating artificial sea caves with air turbine equipped blow holes (OceanLinx). “Articulating raft” and OWC type WECs require large horizontal plane surface areas per unit of intercepted wave front width that increases WEC vessel volume, mass and hence capital costs. Another downside to these designs is that they primarily capture only “heave” or vertical component wave energy (only 50% of total wave energy in deep water). Point-absorber, buoy-type, and other “surface-area-dependent” WECs also have extremely poor (actually negative) economies of scale. When their capture widths are doubled to intercept twice the energy containing wave front, their volumes, weights, and hence costs are tripled increasing rather than decreasing their capital cost per kilowatt captured.
While several early WEC concepts (including the early Salter Duck of the University of Edinburgh) did propose the use of elongated floats, or groups of adjacent floats, oriented parallel to (facing) wave fronts to intercept and capture more wave energy per unit float width, volume, and cost, few wave front parallel “wave barrier” or “wave terminator” type WECs are currently being pursued. This is primarily due to their severe sea survival vulnerabilities. One notable exception are “surge flap” type WECs that use a buoyant, vertically oriented (in still water) elongated flap or panel, hinged at its base that rotates about the hinge in response to lateral (surge) wave forces. This design is currently being developed by Aquamarine, Resolute, Langlee and others. Most “surge flap” WECs are of fixed orientation (toward the prevailing wave front direction), hinged at or near the seabed, in near-shore locations having less than 20 meters water depth (except for the Langlee design that uses two parallel buoyant flaps hinged to a semi-submerged frame).
The “single elongated arm”, “dual swing arm” or “compound-motion swing arm” float-to-frame linkages of the disclosure substantially improve the performance of all “surge flap” type WECs in two ways. The first is to improve the flap's surge wave energy capture effectiveness by allowing the lower portion of the flap (near the fixed bottom hinge) to move laterally. The second improvement is to enable the buoyant flaps to also capture substantial heave (vertical component) wave energy by allowing increased concurrent horizontal and vertical flap movement or translation.
It is most desirable to have WECs with floating bodies operate on the ocean surface in deep water (offshore) where the wave energy resource is greatest and siting conflicts are minimized. WECs with elongated surface floats oriented parallel to wave fronts can intercept and potentially absorb several times more wave energy per cubic meter of float volume, weight, and cost. Few WECs of this type have been proposed or pursued to date, however, because WECs with elongated surface floats oriented parallel to wave fronts must survive broadside impacts against these surface floats from storm waves that can reach 15 meters height. Several proposed WECs operate fully submerged using only wave induced hydrostatic pressure fluctuations. They are deployed either on the seabed (M3), or substantially below the surface (CETO and AWS II), but wave energy, predominantly a surface phenomenon, decreases exponentially with depth. Thus, subsurface deployed WECs can only access the heave wave energy component (only 50% of total wave energy at the surface), which results in low wave energy capture efficiencies.
Many embodiments of the disclosure overcome the survival limitations of prior elongated float, surface deployed WECs by using various methods to totally submerge the floats during severe sea conditions including those described and claimed in my U.S. Pat. No. 8,614,520 and in my prior regular utility application Ser. No. 14/101,325, of which this application is a Continuation-In-Part. The present disclosure also describes and claims several ways to link the wave front parallel oriented elongated floats to stabilizing frames or structures and WEC Power-Take-Off (PTO) systems in ways that increase the wave induced horizontal, vertical and/or rotational translation of such surface floats and, therefore, their wave energy capture efficiency.